1. Field of the Invention
The present invention relates to the manufacture of aqueous electrochemical devices, and more particularly, electrochemical devices in which the aqueous based electrolyte is maintained in a solid form.
2. Description of the Prior Art
Electrochemical devices having aqueous electrolytes are well known in the art. Examples of such cells include traditional LeClanche cells, Ni-Cd, Ni-Zn, Zn-MnO.sub.2, Ni-H.sub.2 and Pb-acid cells. These cells typically include an anode material a cathode material, a liquid aqueous electrolyte material and a solid separator. In a typical configuration, the separator is located between the anode and the cathode within the electrolyte. The separator, which is solid in nature, functions to prevent spontaneous discharge by providing a barrier against direct contact of the anode material with the cathode material. The separator can also impede the transport of active materials between the electrodes to prevent dendrite formation in the case of secondary batteries.
Because of the liquid nature of the electrolyte material, it is necessary to maintain the separator in solid form. Examples of materials useful as separators include cotton, nylon, polypropylene, cellulose rayon paper, cellulose nylon paper, polyethylene, polyvinylchloride, polytetrafluoroethylene, polysulfone, cellophane, and the like. These materials are typically maintained in a woven or non-woven membrane form. The inclusion of the separator in the cells, while necessary, is problematical in that it may not be chemically compatible with the liquid electrolyte thereby reducing battery life, may increase the impedance of the cell or may be complex and costly to manufacture. Accordingly, attempts are being made in the art to try to improve the performance of the separator material and the separator/electrolyte element.
For example, U.S. Pat. Nos. 4,262,067 and 4,218,280, assigned to United States of America (NASA), disclose battery separator membranes which are crosslinked. More particularly, an aqueous solution of a film-forming material, such as polyvinyl alcohol is admixed with a crosslinking agent having a basic pH, the admixture is formed into a desired physical shape by casting and the like, the sheet is dried to form a self-supporting film and is immersed in an aqueous acid solution to effectuate crosslinking. After crosslinking, the completed separator material is immersed in an electrolyte solution including a conductive compound such as KOH. Although this type of separator has advanced separator properties, after the immersion of the separator into the KOH solution, the resulting material is a multi-phase material (i.e. a liquid supported in a solid matrix). This separator is potentially difficult to fabricate.
Japanese published application numbers 56-116274 and 55-105969 both disclose separators for use in alkaline electrochemical cells wherein radiation curing is utilized to form the separator. Following curing, the separator is immersed in a liquid electrolyte material to produce a multiphased electrolyte/separator material.
In the field of solid state alkali metal anode cells having non-aqueous electrolytes, cells have been produced without requiring the presence of an independent separator. More particularly, these cells utilize a solid electrolyte which is interposed between an anode layer and a cathode layer. Due to the solid nature of the electrolyte, it serves the dual function of being an electrolyte and a separator. Examples of such cells are disclosed in U.S. Pat. No. 4,792,504, assigned to MHB Joint Venture.
So called gelled electrolytes may be utilized in association with alkaline batteries or lead acid batteries. These materials are particularly used in alkaline batteries to reduce electrolyte dissolution and in lead acid batteries for reducing self discharge. Example of suitable gelled electrolydes are disclosed in the following references. Manufacture of Laminar Battery, Hino, Yoshihisa,; Takayanagi, Hiroyuki; Yoshioka, Michie; Jpn. Kokai Tokkyo Koho JP 61-93,544 [86-93,554] 12 May 1986; Dry-Cell Batteries, Shinoda, Kenichi; Ota, Hirokiko; Takeshima, Takaoki; Kinoshita, Masaaki; Watanabe, Nobuaki; Jpn. Kokai Tokkyo Koho JP 62-164,558 [87-154,558] 09 Jul 1987; Hydrogen Battery Anodes. Mitsuyasu, Kiyoshi; Tsuruta, Shinji; Sato, Yuji; Kanda. Motoi; Yagasaki, Eriko; Jpn. Kokai Tokkyo Koho JP 62-265,556 [87-264,556] 17 Nov. 1987; Gelled Electrolytes for Lead-Acid Batteries. Morita, Yoshishige; Jpn. Kokai Tokkyo Koho JP 62-264,571 [87-264,571] 17 Nov. 1987; Sealed Lead-Acid Batteries with Polymer-Covered Cathodes Inoe, Toshihiro; Matsuo, Kojira; Jpn. Kokai Tokkyo Koho JP 63-126,174 [88-126,174] 30 May 1988; and Lead-Acid Batteries with Gelled Electrolytes, Takahashi, Wataru; Kamiharashi, Seiji; Jpn. Kokai Tokkyo Koho JP 63-152,881 [88-152,881] 25 Jun 1988.
To date, electrochemical cells having aqueous electrolytes have required the presence of an independent separator material. Accordingly, there exists a need in the art for developing electrochemical cells containing aqueous electrolytes wherein the cells do not require the presence of an independent separator material.